This invention relates to logic circuitry and in particular to driver circuitry which provides output voltage levels which are essentially the same as the levels of power supplies used with the circuitry.
Many of today's digital integrated circuits use field effect transistors which have a threshold voltage which must be exceeded before the transistor turns ON. This results in at least one of the two output logic levels being a threshold voltage below one of the potential levels of power supplies used with these circuits. It is desirable in some cases to have a full output voltage (logic levels which are the same as the levels of the used power supplies). One solution to threshold voltage losses is driver circuits which use bootstrap capacitors with delay circuits to first charge a terminal to a potential close to a power supply level and then thereafter to capacitively bootstrap the potential level of the terminal to a potential level which is above the level of power supply. One problem with this solution is that the delay introduced by the delay circuits may vary with processing variations differently than the rest of the circuit. This can result in both terminals of the bootstrap capacitor increasing or decreasing in potential at essentially the same time. This can cause the desired output voltage level not to be reached.
It is desirable to have driver circuitry which uses a bootstrap capacitor and delay circuitry in which the delay associated with the delay circuitry is controlled by the terminal of the circuitry which is to be bootstrapped in potential. This would limit the adverse effect of processing variations on the performance of the driver circuitry.